etymology - Where does the suffix 〜がる come from?

I've read that several bits of Japanese come from contractions with ある:

• だ comes from で + ある (source)


• なる comes from に + ある (source)


• たり comes from て + あり (source)


• たり comes from と + あり (source)


• Adjective forms like たのしかった come from inflecting たのしく + ある (source)

(My apologies if I've made any mistakes in the above list!)

Because contraction with ある seems to have occurred quite a few times, I started wondering if the suffix 〜がる (as in たがる or ほしがる) was a contraction of が + ある. I realize this is baseless speculation, but it sounded plausible to me, so I tried to look it up to see if it was right. Unfortunately, I couldn't find anything about the etymology of がる online, and my dictionaries don't say anything on the subject either.

Is this possible?

Is there a better explanation?

Answer

This paper breifly lists this as a source:

「がる」の語源にはいくつかの可能性があるようだが [...] 日本国語大辞典によると、　「アハレガル、ウレシガル、痛ガル、面白ガルのガルは情をそそられる意から、アガルの約。道心ガル、才子ガル、得意ガルのガルは、ゲ（気）アルの約〔大言海〕」などの紹介がある。

I do not have access to 日本国語大辞典, but it seems it does not support your がある theory, rather suggests that it derives from あがる and/or 気{げ}ある.